Techniques, apparatus and systems described herein can be used in various wireless access technologies such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc.
The CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may be implemented with a radio technology such as Global System for Mobile communications (GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE).
The OFDMA may be implemented with a radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved-UTRA (E-UTRA) etc. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved-UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE employs the OFDMA in downlink and employs the SC-FDMA in uplink. LTE-advance (LTE-A) is an evolution of the 3GPP LTE. For clarity, this application focuses on the 3GPP LTE/LTE-A.
However, technical features of the present invention are not limited thereto.
In FIG. 1, a radio frame includes 10 subframes. A subframe includes two slots in time domain. A time for transmitting one subframe is defined as a transmission time interval (TTI). For example, one subframe may have a length of 1 millisecond (ms), and one slot may have a length of 0.5 ms.
One slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain. Since the 3GPP LTE uses the OFDMA in the downlink, the OFDM symbol is for representing one symbol period. The OFDM symbol may also be referred to as an SC-FDMA symbol or a symbol period.
A resource block (RB) is a resource allocation unit, and includes a plurality of contiguous subcarriers in one slot. The structure of the radio frame is shown for exemplary purposes only. Thus, the number of subframes included in the radio frame or the number of slots included in the subframe or the number of OFDM symbols included in the slot may be modified in various manners.
In FIG. 2, a downlink slot includes a plurality of OFDM symbols in time domain. It is described herein that one downlink slot includes 7 OFDM symbols, and one resource block (RB) includes 12 subcarriers in frequency domain as an example. However, the present invention is not limited thereto.
Each element on the resource grid is referred to as a resource element. One RB includes 12×7 resource elements. The number NDL of RBs included in the downlink slot depends on a downlink transmit bandwidth. The structure of an uplink slot may be same as that of the downlink slot.
In FIG. 3, a maximum of three OFDM symbols located in a front portion of a 1st slot within a subframe correspond to a control region to be assigned with a control channel. The remaining OFDM symbols correspond to a data region to be assigned with a physical downlink shared chancel (PDSCH). Examples of downlink control channels used in the 3GPP LTE includes a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of a subframe and carries information regarding the number of OFDM symbols used for transmission of control channels within the subframe. The PHICH is a response of uplink transmission and carries an HARQ acknowledgment (ACK)/not-acknowledgment (NACK) signal. Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes uplink or downlink scheduling information or includes an uplink transmit (Tx) power control command for arbitrary UE groups.
The PDCCH may carry a transport format and a resource allocation of a downlink shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information on a paging channel (PCH), system information on the DL-SCH, a resource allocation of an upper-layer control message such as a random access response transmitted on the PDSCH, a set of Tx power control commands on individual UEs within an arbitrary UE group, a Tx power control command, activation of a voice over IP (VoIP), etc.
A plurality of PDCCHs can be transmitted within a control region. The UE can monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate based on a state of a radio channel. The CCE corresponds to a plurality of resource element groups.
A format of the PDCCH and the number of bits of the available PDCCH are determined according to a correlation between the number of CCEs and the coding rate provided by the CCEs. The BS determines a PDCCH format according to a DCI to be transmitted to the UE, and attaches a cyclic redundancy check (CRC) to control information.
The CRC is masked with a unique identifier (referred to as a radio network temporary identifier (RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UE may be masked to the CRC. Alternatively, if the PDCCH is for a paging message, a paging indicator identifier (e.g., paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is for system information (more specifically, a system information block (SIB) to be described below), a system information identifier and a system information RNTI (SI-RNTI) may be masked to the CRC. To indicate a random access response that is a response for transmission of a random access preamble of the UE, a random access-RNTI (RA-RNTI) may be masked to the CRC.
In FIG. 4, an uplink subframe can be divided in a frequency domain into a control region and a data region. The control region is allocated with a physical uplink control channel (PUCCH) for carrying uplink control information. The data region is allocated with a physical uplink shared channel (PUSCH) for carrying user data. To maintain a single carrier property, one UE does not simultaneously transmit the PUCCH and the PUSCH. The PUCCH for one UE is allocated to an RB pair in a subframe. RBs belonging to the RB pair occupy different subcarriers in respective two slots. This is called that the RB pair allocated to the PUCCH is frequency-hopped in a slot boundary.
In FIG. 5, a wireless communication system includes a BS(10) and one or more UE(20). In downlink, a transmitter may be a part of the BS(10), and a receiver may be a part of the UE(20).
In uplink, a transmitter may be a part of the UE(20), and a receiver may be a part of the BS(10). A BS(10) may include a processor (11), a memory (12), and a radio frequency (RF) unit (13). The processor (11) may be configured to implement proposed procedures and/or methods described in this application. The memory (12) is coupled with the processor (11) and stores a variety of information to operate the processor (11). The RF unit (13) is coupled with the processor (11) and transmits and/or receives a radio signal.
A UE(20) may include a processor (21), a memory (22), and a RF unit (23). The processor (21) may be configured to implement proposed procedures and/or methods described in this application. The memory (22) is coupled with the processor (21) and stores a variety of information to operate the processor (21). The RF unit (23) is coupled with the processor (21) and transmits and/or receives a radio signal. The BS(10) and/or the UE(20) may have single antenna and multiple antenna. When at least one of the BS (10) and the UE(20) has multiple antenna, the wireless communication system may be called as multiple input multiple output (MIMO) system.
In a 3GPP LTE system, there are two types relay node.
A type II relay node (RN) cannot transmit its own common RS (CRS) as it does not have a separate cell ID and appears as a part of the donor eNB at least to Rel-8 UEs. Thus, it is assumed in prior arts that a type II RN does not transmit CRS but uses dedicated RS (DRS) to assist the demodulation of PDSCH transmitted by RN.
FIG. 6 illustrates an example of the prior arts: At subframe n, a eNB tries initial transmissions of PDSCH to UEs, and RNs overhear these transmissions for data relaying at subframe (n+k). A UE1, a Rel-8 UE to be served by RN1 at subframe (n+k), is configured to be in the DRS mode. At subframe (n+k), RNs transmits the overheard PDSCH without transmitting CRS. As no CRS is transmitted by a RN1, we have no choice but to rely on DRS in transmitting PDSCH to the UE1. RS defined in Rel-10 can be used for the PDSCH transmission to a UE2 which is a Rel-10 UE.
As type II RN does not transmit PDCCH, the scheduling information for each PDSCH/PUSCH is transmitted from eNB. This means that a type II RN forwards PDSCH/PUSCH according to the scheduling decision made by the centralized scheduler located in eNB.
Therefore, it is required to design PDSCH/PUSCH forwarding procedures that define the transmission timing of relevant signals including control information and relayed data in consideration of the half-duplex operation of RN.
Also, RN which receives PUSCH from a UE should forward the decoding result (and/or the decoded PUSCH) to eNB prior to the PHICH transmission timing in order for eNB to generate PHICH ACK or NACK. However, as the UE expects the fixed PHICH timing in 3GPP LTE system, it is difficult for RN to deliver the PUSCH decoding result to eNB in advance.
The eNB cannot utilize the RN's decoding result in generating the corresponding PHICH content (ACK or NACK) while keeping the predetermined PHICH timing.
Thus, a solution is required to resolve this PHICH transmission problem in the case of Type II relay.